1. FIELD OF THE INVENTION
This invention relates to a sewing machine control device which automatically releases the cloth presser of a sewing machine.
2. BACKGROUND ART
In general, in a sewing operation with a sewing machine, the thread cutter, the thread wiper and the cloth presser of the sewing machine are restored before a material which has been sewed (hereinafter referred to as "a sewn cloth") is removed from the sewing machine. Most of the industrial sewing machines are so designed that these operations are automatically carried out. That is, the thread cutting operation is carried out while the needle is moved from its upper position to its lower position. Thereafter, in order to stop the movement of the needle when the needle is moved to its upper position, the output shaft of a sewing machine drive motor is braked, while the thread wiping operation is performed. Then, after the brake is released, the cloth presser is restored (returned to its original position) and the sewn cloth is removed from the sewing machine.
In one type of sewing method, when the sewing operation of one piece of cloth is accomplished, another piece of cloth is immediately sewn thereafter. In this sewing method, no thread cutting operation is required. Therefore, some of the sewing machines are so designed as to selectively employ the thread cutting function.
In the case of a conventional control device operating as described above, the cloth presser is released after the needle is completely stopped at the upper position. That is, although the thread cutting operation and the thread wiping operation have been accomplished, the cloth is still pressed, and accordingly the sewn cloth cannot be removed from the sewing machine before the braking operation is accomplished, which makes it difficult to improve the working efficiency.
Even in the case where the thread cutting operation and the thread wiping operation are not required, the removal of the sewn cloth is permitted only after the braking operation is ended, which also makes it difficult to improve the working efficiency.
The working efficiency may be improved by shortening the brake operation time. However, in this case, it may become impossible to completely stop the needle, and the operation of the sewing machine may have safety difficulties.